Controlling an automatic transmission

Abstract

A method of downshifting an automotive transmission. An on-coming transmission element is stroked while pressure for an off-going element is reduced. Pressure for the stroked on-coming element is increased to be sufficient to carry torque. Pressure for the off-going element is reduced below a torque transmitting amount once the stroked on-coming element has a sufficient torque carrying capacity. Torque capacities for the elements are determined from transmission output torque and acceleration and transmission input torque and acceleration. Feed forward or feedback terms for off-going and on-coming element torque capacities may be calculated using the transmission output torque, transmission input acceleration, and transmission input torque.

The invention claimed is: 
     
       1. A method of controlling an automatic transmission comprising:
 stroking an on-coming element while pressure for an off-going element is reduced; 
 increasing pressure for the stroked on-coming element before reducing pressure for the off-going element below a torque transmitting amount once the stroked on-coming element has a torque capacity sufficient to shift gear ratios, torque capacities for the elements being determined from transmission output torque and acceleration and transmission input torque and acceleration. 
 
     
     
       2. The method of  claim 1  further comprising:
 increasing pressure for the stroked on-coming element based on the transmission output torque, a shift rate, and approximating a torque capacity for the on-coming element as zero. 
 
     
     
       3. The method of  claim 1  further comprising:
 adjusting, while reducing pressure for the off-going element below the torque transmitting amount, the on-coming element pressure and transmission input torque based on the transmission output torque and a shift rate. 
 
     
     
       4. The method of  claim 1  further comprising:
 completing shifting gear ratios by adjusting the transmission input torque and pressure for the on-coming element based on the transmission output torque, a shift rate, and reducing a torque capacity of the off-going element to zero. 
 
     
     
       5. The method of  claim 1  further comprising:
 completing shifting gear ratios by adjusting the transmission input torque and pressure for the off-going element based on the transmission output torque, a shift rate, and adjusting a torque capacity of the on-coming element to produce a zero slip condition. 
 
     
     
       6. The method of  claim 1  further comprising:
 completing shifting gear ratios by adjusting pressure for the off-going and on-coming elements based on a demanded torque, the transmission output torque, and a shift rate. 
 
     
     
       7. A method of controlling an automatic transmission comprising:
 reducing an off-going torque capacity to a first capacity and adjusting an engine torque to a first torque, in response to a downshift from a current to a new gear ratio, the first capacity and torque based on an on-coming torque capacity approximated as zero, transmission output torque, and shift rate; 
 adjusting the on-coming torque capacity to an undetectable capacity greater than a stroke capacity while simultaneously increasing the off-going torque capacity from the first capacity to a second capacity based on the on-coming torque capacity approximated as zero, transmission output torque, and shift rate; 
 increasing the on-coming torque capacity from the undetectable capacity to a measureable capacity and adjusting the off-going torque capacity from the second capacity to a holding capacity based on the transmission output torque and shift rate; 
 reducing the off-going torque capacity from the holding capacity to zero while adjusting, based on the transmission output torque and shift rate, the engine torque and on-coming torque capacity from the measurable capacity. 
 
     
     
       8. The method of  claim 7  further comprising:
 increasing, prior to reducing the off-going torque capacity to the first capacity, the on-coming torque capacity to above a stroke capacity before decreasing the on-coming torque capacity to zero. 
 
     
     
       9. The method of  claim 7  further comprising:
 completing the downshift by adjusting the on-coming torque capacity and engine torque based on the off-going torque capacity reduced to zero, transmission output torque, and shift rate. 
 
     
     
       10. The method of  claim 7  further comprising:
 completing the downshift by adjusting the off-going torque capacity and engine torque based on the on-coming torque capacity adjusted to a zero slip capacity, transmission output torque, and shift rate. 
 
     
     
       11. The method of  claim 7  further comprising:
 completing the downshift by adjusting the off-going and on-coming torque capacities based on the transmission output torque, shift rate, and a demanded torque. 
 
     
     
       12. The method of  claim 7  further comprising:
 adjusting the on-coming torque capacity to be sufficient to complete the downshift based on a measured transmission output torque, a measured transmission input torque, a measured transmission output acceleration, and a measured transmission input acceleration. 
 
     
     
       13. The method of  claim 7  further comprising:
 adjusting a torque capacity of a transmission friction element based on a measured transmission output torque, a measured transmission input torque, a measured transmission output acceleration, and a measured transmission input acceleration. 
 
     
     
       14. The method of  claim 7  further comprising:
 approximating the on-coming torque capacity as an actual measured on-coming torque capacity. 
 
     
     
       15. A method of controlling an automatic transmission comprising:
 reducing an off-going torque capacity to a first capacity and adjusting an engine torque to a first torque, in response to a downshift from a current gear ratio to a new gear ratio, the first capacity and torque based on an on-coming torque capacity approximated as zero, transmission output torque, and shift rate; 
 adjusting the on-coming torque capacity to a new capacity to produce an intermediate gear ratio within a range of the new gear ratio; 
 engaging a dog clutch while an off-going element is slipping; 
 detecting the on-coming torque capacity exceeds a minimum capacity to complete the downshift; 
 completing the downshift when the minimum capacity is detected. 
 
     
     
       16. The method of  claim 15  further comprising:
 completing the downshift by adjusting the engine torque based on reducing the off-going torque capacity to zero, transmission output torque, and shift rate. 
 
     
     
       17. The method of  claim 15  further comprising:
 completing the downshift by adjusting the off-going torque capacity based on a demanded torque, the transmission output torque, and the shift rate. 
 
     
     
       18. The method of  claim 15  further comprising:
 adjusting the on-coming torque capacity based on a measured transmission output torque, a measured transmission input torque, a measured transmission output acceleration, and a measured transmission input acceleration. 
 
     
     
       19. The method of  claim 15  further comprising:
 adjusting a torque capacity of a transmission element based on a measured transmission output torque, a measured transmission input torque, a measured transmission output acceleration, and a measured transmission input acceleration. 
 
     
     
       20. The method of  claim 15  further comprising:
 approximating the on-coming torque capacity as an actual measured on-coming torque capacity.